In recent years, high-speed infrared communications, such as IrSS (one-way communications function (Home Appliance Profile) that conforms with IrSimple 1.0 standards), have come into use for transmitting image data for pictures taken by cell phones, digital cameras, etc., to display devices, such as liquid crystal televisions, thereby displaying the pictures, or transmitting and storing such image data to, for example, hard disk recorders. Infrared output power for use in such infrared communications is lower than that from remote controls for controlling electronic equipment.
On the other hand, emission-line peaks for argon (Ar) and mercury (Hg) gases enclosed in cold cathode fluorescent lamps (CCFLs) (hereinafter, referred to as “lamps”) for use as backlights in liquid crystal televisions correspond to rays of near-infrared light having a wavelength of 900 nm to 950 nm. In some cases, such near-infrared light leaks outside the liquid crystal television, and enters a light-receiving portion of an infrared communications receiver included in the liquid crystal television after being reflected by a viewer or a peripheral object.
In the case where a plurality of lamps are driven by continuous drive, the lighting frequency of the lamps is 1 MHz, and therefore the frequency of near-infrared light emitted by the lamps is also approximately 1 MHz. However, rays of near-infrared light emitted by the lamps differ in phase, and therefore overlap with one another so that their optical strengths do not change substantially. When the near-infrared light with a substantially unchanging optical strength enters the light-receiving portion of the receiver simultaneously with infrared light for use in infrared communications, the near-infrared light turns into continued noise with a substantially unchanging strength (hereinafter, referred to as “continuous noise”). However, when processing a data signal containing continuous noise, a frequency filter portion in the receiver can reduce the continuous noise to a sufficiently low level. Therefore, the continuous noise does not prevent reception of the data signal.
On the other hand, when the lamps are driven by PWM (Pulse Width Modulation) drive, for example, as in the case where backlights are driven by dimming drive, an oscillator for generating a lighting frequency of 1 MHz for the lamps is required to be turned ON/OFF at a frequency of, for example, 100 kHz. In such a case, a phenomenon is known to occur where not only near-infrared light is generated when the oscillator is turned ON but also near-infrared light with an abruptly changing optical strength is generated about once every ten times when the oscillator is switched from OFF to ON. The near-infrared light with an abruptly changing optical strength has a frequency of about 10 kHz and a pulse width corresponding to a frequency of 1 MHz.
The near-infrared light enters the light-receiving portion of the receiver simultaneously with the infrared light for use in infrared communications, and turns into noise (hereinafter, referred to as “abrupt noise”) including pulses with abruptly changing strengths. On the other hand, the near-infrared light that is emitted when the lamps are being driven at 1 MHz turn into noise (hereinafter, referred to as “non-abrupt noise”) including no abruptly changing pulses even when the near-infrared light enters the light-receiving portion. Unlike the non-abrupt noise, the abrupt noise is difficult to reduce to a sufficiently low level using the frequency filter portion.
Therefore, conventionally, in order to prevent entry of near-infrared light from lamps that has an abruptly changing optical strength into the light-receiving portion of the receiver, optical filters for absorbing near-infrared light are affixed around the lamps.
Also, Patent Document 1 discloses a receiver including a reception status determination portion which, upon reception of a data signal transmitted from a remote control, determines whether the reception of the data signal is good or not, and when the reception is poor, controls a dimmer portion to cancel PWM drive.
Patent Document 2 discloses an optical receiver in which a light-receiving portion provided therein has an optical filter attached thereto such that, when the light-receiving portion receives an infrared signal transmitted from a remote control, near-infrared light emitted by a display device is unlikely to enter the light-receiving portion after being reflected by clothes of a viewer or a peripheral object.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-352394    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2006-41657